Acoustoelectrically Enhanced Phonon-Photon Emitter-Receivers

Compact signal processing elements such as amplifiers, filters, and delay lines, are difficult to implement in all-optical schemes. The much slower phase velocity of GHz surface acoustic waves compared to telecom photons provides a pathway to implement these functions at chip scale. By driving surface acoustic waves in SiN rib waveguides on lithium niobate on insulator through optical forces arising from radiation pressure and the photoelastic effect, we demonstrate a photonic–phononic emitter–receiver (PPER) architecture that transduces frequency-encoded optical signals into the acoustic domain and back. Two optical tones launch a surface acoustic wave perpendicular to the emitter waveguide, which propagates to a receiver waveguide where the encoded information is re-imprinted onto an optical pump. This scheme enables broadband transduction across a continuum of frequencies, extending beyond the limits of inter-digital transducers. To probe and enhance acousto-electric interactions at these high frequencies, an InGaAs film is placed between the two waveguides. The strong piezoelectric coupling of the acoustic wave, creates a copropgating electric field, causing periodic charge bunching within the semiconductor film. When a DC bias is applied, this yields acoustic gain as the electron drift velocity surpasses the acoustic phase velocity. In addition, the bias-induced modulation of acoustic velocity provides a mechanism for tunable phase shifting, which combined with a PPER enables controllable optical signal delay.